Magnolia Allelopathy

You know that you are in the South when the magnolia fragrance is in the air.  The magnolia is symbolic of the South, and is one of the most popular trees seen in Huntsville.  The shade from the dense canopy is welcome during the hot Alabama summers, but the magnolia is not as hospitable to the plants trying to grow around its roots.

Most people think of the magnolia with large, glossy leaves and enormous, white blossoms.  Not many trees can match its beauty. It does, however, have its drawbacks.  Dense shade and shallow roots make it impossible to grow grass beneath the canopy. The roots often crack and lift the pavement if the tree is planted between a sidewalk and curb. The roots can also get under foundations, and cause expensive structural damage, so be careful not to plant them too close to a house.  They can grow up to 40 feet wide, so they take up a lot of space.  The worst part of all is that the leaves continuously drop all year long, adding leaf removal to the everyday to-do list. 

Allelopathy is the suppression of growth of one plant species by another due to the release of toxic substances.  Magnolias secrete allelopathic sesquiterpene lactones, costunolide and parthenolide, that discourage competition for water and nutrients.  Also, its deep shade limits the plants that thrive under a magnolia tree.

Many people in Huntsville have never heard of magnolia allelopathy, and plant magnolia trees in a spot where they want a nice lawn.  Ten years later, they can’t figure out why their grass is dead and call their lawn care service and want to know what to do about the problem.  The advice is usually to call a tree service and cut down the tree. 

Choose a planting site carefully. Most types are hard to move once established, and many grow very large. The best soil for magnolias is fairly rich, well drained, and neutral to slightly acidic. 

Have you noticed how difficult it is to grow grass, or anything else under a magnolia tree?  Take my advice - Don’t plant a magnolia tree where you want a nice lawn.